Conventionally, a power transmission device that transmits a rotation driving power, outputted from a driving source, to a driving target device is known. This kind of power transmission device is required to have a function to block transmission of a rotation driving power quickly in order to prevent the driving source from being subjected to an undue load when the driving target device is locked by burning or the like.
For example, in Patent Document 1, disclosed as a power transmission device, which transmits a rotation driving power outputted from a vehicle-travelling engine that is a driving source to a compressor of a vehicular refrigeration cycle that is a driving target device, is one that has a torque limiter to block transmission of the rotation driving power by being broken when a torque transmitted from the engine to the compressor exceeds a predetermined torque.
More specifically, the power transmission device of Patent Document 1 includes a pulley rotated by the rotation driving power outputted from the engine, an inner hub linked with a rotation shaft of the compressor, and a damper made of rubber that is an elastic material and is used as an linking elastic member linking the pulley with the inner hub, and the torque limiter is configured by providing a breakage portion in a part of the inner hub.
The breakage portion is broken, and a part of the inner hub is separated from the rotation shaft of the compressor when the torque transmitted from the engine to the compressor exceeds the predetermined torque. Accordingly, the rotation driving power outputted from the engine is prevented from being transmitted to the compressor.
The damper gives a load on the inner hub in a direction away from the rotation shaft of the compressor while the breakage portion is not broken. After the breakage portion is broken, the damper displaces a part of the inner hub separated from the rotation shaft of the compressor in the direction away from the rotation shaft of the compressor. Therefore, after the breakage portion is broken, noise generation caused by contact between the part of the inner hub separated from the rotation shaft of the compressor and the rotation shaft of the compressor is limited.